With the huge air flow capacity of the APS turbochargers utilized in the APS Intercooled Twin Turbo High Output System, the unique APS High Volume Twin Vent Blow Off Valve delivers unsurpassed venting performance, excellent driveability and crisp turbocharger response in on/off throttle applications. A blow off valve is a device that releases pressure from the turbocharger when the throttle is released. It ensures that the pressure shock load on the turbocharger compressor is minimized and encourages each turbocharger rotating group to continue spinning during gear changes. This ensures that when the next gear is selected and the throttle re-applied, both turbochargers rapidly produce high boost pressure and strong torque. With a large or twin turbochargers, releasing pressure from the turbine compressor wheel when the throttle is snapped shut is critical not only for lightning fast turbocharger response, but for turbocharger longevity. A huge volume of air must be passed through the blow off valve as soon as the throttle is closed. Most blow off valves have limitations in their design that inhibit the level of performance demanded by APS. Piston/bore diameter and venting ports are often too small and surprisingly, most will not fully expose the exhaust ports when fully opened. APS designed the APS high volume twin vent blow off valve specifically for the APS Intercooled Twin Turbo LS1. A mammoth 1.417" (36 mm) internal bore size delivers huge capacity and at full piston travel, all ports are fully exposed for maximum blow off volume. The APS twin vent BOV features 30 micron hard anodized, T6 billet aluminium body, low friction bronze piston, all stainless steel hardware including spring and Viton 'O' rings. The large primary vent is designed to plumb back into the inlet tract and ensures the best driveability during cruise conditions. More importantly the APS BOV cures the problems seen with after market 100% external venting blow off valves. And under spirited driving conditions with turbochargers running high boost pressure levels, the APS twin vent blow off valve continues to vent through to the second stage port in order to expel the maximum amount of charge air possible. Fine adjustment to blow off valve operation can be performed through the actuation adjustment screw for optimum configuration. The above animation demonstrates the operation of the APS High Volume Twin Vent Blow Off Valve. The three modes of operation include: Ports Closed - Under open throttle conditions where turbocharger boost pressure is required, the bronze BOV piston is held shut in order to supply the maximum amount of charge air to the engine Primary Port Open - Under light load conditions where the throttle opening has been reduced or shut, the piston moves partially up the bore travel and opens the primary port to vent charge air back into the inlet tract. This ensures smooth engine operation and alleviates the rich condition and subsequent backfire when utilizing a BOV construction that vents100% of charge air to atmosphere. Both Ports Open - Under high load conditions where the throttle has been shut, the piston travels fully so that both the primary and the wide mouth secondary ports open to vent the maximum charge air possible. Air vented through the primary port is routed back into the inlet tract. In addition, additional excess charge is air vented through the wide mouth secondary port to atmosphere. To see more components for the Holden - HSV LS1 click HERE If you would like further information on the APS Intercooled Twin Turbo System for the Holden LS1 Commodore and HSV cars, please do not hesitate to contact Autotech Engineering via email on on sales@autotechengineering.com.au or by phone on (02)9897 1378